The present invention relates to mining equipment, and more specifically to a launch platform for a high wall miner and conveyor cars and a method of high wall mining.
In high wall mining, for example of a coal seam in a mountain, a notch is cut in the side of the mountain at the elevation of the coal seam. This forms a flat surface, known as a bench, to work from and move equipment on, and a wall or face along which mine entries, also called shafts or rooms, are made into and along the coal seam. On the bench, a launch platform, also referred to as a table or deck, is used to push a continuous mining machine, also called a miner, forward against the high wall formed by the notch, cutting a mine entry horizontally into the coal seam.
As the miner is moved deeper in the coal seam, a coal conveyor car (for example, with a continuous web, belt, auger, or other conveyance to take away coal) is added behind the mining machine, and then behind each subsequent car, forming a mining string providing a continuous conveyor to remove coal as the miner cuts deeper into the wall. More specifically, generally a pair of cylinders, for example, hydraulic cylinders, can push each side of the miner and the subsequent conveyor cars connected in a string behind the miner. Often the maximum depth of the horizontal mine entry into the coal seam is limited by the length of the string formed by the cars behind the miner that can be effectively pushed by the hydraulic cylinders on the launch platform, for example, about 950 feet deep. Often the conveyor cars simply skid on the ground and thus significant friction and resulting resistance to advancement develops as more and more cars are added to the string behind the miner. Additionally, the maximum depth of the mine entry into the coal seam can be limited by the electrical current loss experienced in an excessively long power cable used to drive the mining head on the miner, for example, over about 800 feet of cable.
When the end of the coal seam or the maximum length of mining with the system used is reached, the conveyor cars are extracted one by one from the mine entry using the same launch platform and the same hydraulic cylinders. The extracted conveyor cars must be unhooked from the string, removed from the launch platform, and stowed. Such storage of conveyor cars on the narrow bench can be difficult when several dozen cars are used in a string.
After the miner is extracted, the launch platform is then moved sideways on the bench, along the face of the wall and next to the first mine entry just cut, to cut a target location for a second mine entry, with the second entry preferably extending parallel to the first entry. A pillar or supporting wall of coal is generally left between each pair of mine entries so that the mine entries do not collapse on the mining string under the weight of the overlying formation. However, because the launch platform hydraulic cylinders are used to advance the miner into the coal seam, for example, potentially pushing the miner from behind an 800 or 950 foot string of conveyor cars, it is difficult to ensure the side-by-side entries remain straight and parallel so that the pillars are not cut through into an adjacent entry. Such a cut through or too narrow of a pillar can result in subsidence of the overlying formation, trapping the miner and conveyor cars irretrievably.
Because of the height of a typical launch platform, in order for the miner to be advanced into the level of the coal seam, the bench must be downgraded below the level of the bottom of the coal seam, often by one or more feet. With a typical bench having a depth of 100 or more feet, this extra down downgrading removes a significant amount of material, material which must often be returned in order to again fill the bench and meet environmental and aesthetic requirements, thus greatly increasing the time and expense associated with the mining.
With the above described typical mining system and method, only one mine entry is being worked at any one time. Furthermore, during the extraction of the string after the maximum depth is reached in the coal seam, no coal is being cut or extracted because a second mine entry cannot be started until the entire extraction of cars and the miner is complete from the first mine entry, and the launch platform is moved to a new mine entry location adjacent the first mine entry.